Currently, in downhole applications, there are different types of seals to handle high temperature and pressure applications. The present limits of service of these designs are roughly about 350 degrees Fahrenheit and about 13,500 PSI. Under more severe temperature or/and pressure conditions, the presently known designs have been tested and have failed to perform reliably.
Depending on the application, there are different types of seals for high temperatures or/and pressures. In the case of packers set in high temperature applications, U.S. Pat. No. 4,441,721 asbestos fibers impregnated with Inconel wire are used in conjunction with a stack of Belleville washers to hold the set under temperature extremes. Apart from packers or bridge plugs which require seal activation after placement in the proper position, there are other applications involving seals on tools that have to engage a seal bore receptacle downhole and still need to withstand these extremes of temperature and pressure. In many cases, the tool with the seal to land in a seal bore is delivered on wireline. This means that insertion forces are limited because minimal force can be transmitted from the surface through wireline. In these applications, the limited insertion force is a design parameter that has to be counterbalanced with the frictional resistance to insertion created by the interference of the seal in the seal bore. This interference is built into the design of the seal to allow sufficient contact with the seal bore after insertion for proper seal operation. Clearly if the interference is too great the insertion, particularly with a wireline, will become problematic. On the other hand, reducing the interference can result in seal failure under the proposed extreme conditions of pressure and temperature.
There are other design considerations for seals that engage a seal bore downhole. Clearly, on the trip downhole, the seal is exposed to mechanical contact with well tubulars or other equipment. The materials for the seal must be rugged enough to withstand such mechanical impacts as well as to withstand the temperatures and pressures anticipated in the downhole location.
These seals also need to control extreme pressure differentials in an uphole and a downhole direction. Such seals may be inserted and removed from several seal bores during their service life. The design has to be flexible enough to allow long service periods under such extreme conditions as well as the resiliency to allow removal and reinsertion without damage to the seal or the surrounding seal bore.
FIG. 1 illustrates the current commercially available seal that is promoted for severe duty applications. It illustrates a mirror image arrangement around a central adapter 16. A pair of chevron packing rings 14 are disposed about the adapter 16 and outside of the rings 14 is a back-up v-ring 12 and outside of v-ring 12 is an end ring 10 to complete one half of the mirror image arrangement shown in FIG. 1. The open portions of the v-shaped rings open toward the central adapter in an effort to position the rings to withstand pressure differentials from opposite directions. The rings are made of materials suitable for the anticipated temperatures. Tests at pressure extremes of over 13,500 PSI and temperatures above 350 degrees Fahrenheit revealed that this design was unsuitable for reliable service.
In an effort to improve on the performance of the seal shown in FIG. 1, the design of FIG. 2 was tried. It featured a central o-ring 18 surrounded by a pair of center adapters 20. On either side of the center adapters 20 the arrangement was similar to FIG. 1 except that the orientation of the v-shaped opening were now all away from the central o-ring 18 rather than towards each other as had been the case in the design of FIG. 1. Additionally, there was an alternating pattern of material in the rings 22 and 24 of FIG. 2 as compared to the stacking of rings 14 of a like material as shown in FIG. 1. This design of FIG. 2 showed improved performance in high temperature and pressure conditions but was not to be the final solution. The present invention, an illustrative example of which is discussed in the preferred embodiment below, addresses the temperature and pressure extremes while allowing for insertion using a wireline. It features an internal spring mechanism and a feature that prevents collapse of the spring and the sealing elements under extreme conditions. The opposing members in the assembly are also prevented from engaging each other under extreme conditions. The collapse-preventing feature also has a beneficial aspect of seal centralization as the seal is inserted into the seal bore. Those skilled in the art from a review of the description of the preferred embodiment below and the claims that appear thereafter will readily understand these and other beneficial features of the present invention.